On many storage devices, for example RAID (Redundant Array of Independent Disks) and tape libraries, assigning a device address is required. For example, in a tape library, tape drives could use a serial number for a unique identity within the tape library. This allows the tape library controller to communicate with any tape drive in the system, but the library controller does not have information on the physical tape drive location.
The host uses the address when commanding the tape library controller to place a tape cartridge into the drive the host needs to use. The tape library controller can communicate with all the tape drives because they have a unique communication address, but the tape library controller does not know where any of the drives are located.
When the tape library controller gets a host command to load a tape cartridge into a drive at specific address, the tape library controller needs to communicate with that specific drive address to get the drive status. The drive status tells the tape library controller information like, whether the drive can be loaded, or if the load completed, or if error conditions exist. Problems arise because the device address does not correspond to a physical location of the device.
In a RAID system, devices which have errors can be identified by blinking the LED of the failed drive. On larger systems with multiple components such as servers, RAID, Ethernet and Fiber Channel switches, the serial number of the component with an error would be indicated on an operator panel. The difficult task of finding the failed device in the large array of devices is then left to the customer engineer.